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Residual waste – an eternal fire that generates electrical power

Chemical energy is stored in the material used for packaging, carpets and chairs, amongst other things. Some of this energy can be recycled from discarded products. Every year, the Thermische Restabfallbehandlungs- und Energieerzeugungsanlage (TREA) Breisgau (Thermal Residual Waste Treatment and Energy Generation Facility) located in the Breisgau industrial estate close to Freiburg converts around 170,000 t of residual waste into electricity. A gigantic furnace operating at temperatures of up to 1100˚C devours household waste and industrial residual waste. How is this waste turned into electricity? And what of environmental compatibility issues? Dr. Holger Heinig, COO of TREA Breisgau, gives us some insights into a process that harnesses heat and steam and he also talks about future prospects for the cogeneration of power and heat.

Dr. Holger Heinig, Chief Operating Officer of TREA Breisgau © TREA Breisgau

Dr. Heinig, what is TREA Breisgau? 

TREA Breisgau is part of E.ON AG, a company with 90,000 employees around the world. The commercial management of TREA Breisgau and our facilities in Primasens, Neunkirchen, Göppingen, Knapsack and Leudelange (Luxembourg) is the responsibility of our Saarbrücken-based regional centre. TREA Breisgau employs 45 staff. On average, TREA Breisgau burns around 170,000 t of household and household-like industrial waste annually; the facility usually runs 24/7 with the exception of a two- to three-week period set aside for the maintenance and testing of the facility and its equipment. TREA Breisgau turns this waste into electricity. In mid-2011, a drying plant will be erected opposite our building for drying wood and lop. This biomass centre will use part of the heat produced by TREA for the production of wood pellets for energy generation.

How is waste transported to TREA?

All the waste collected from households in the municipal districts of Breisgau-Hochschwarzwald and Emmendingen and the city of Freiburg as well as some of the waste collected in the municipal districts of Ortenau, Rastatt and Baden-Baden is brought to us by the company “Gesellschaft Abfallwirtschaft Breisgau (GAB) mbH. GAB put out a call for tender to European companies relating to TREA Breisgau, and we were commissioned to construct the facility and operate it until 2030. GAB mbH delivers around seventy per cent of the waste processed at TREA; the remaining 30 per cent is waste produced by industrial concerns in the region. When we applied for authorisation to operate the facility, one of the requirements was that transport to the facility should be as environmentally friendly as possible, which involved cutting down on the use of lorries for the transport of waste. Around sixty per cent of all waste is delivered to us by Deutsche Bahn (German Rail).

At TREA Breisgau, waste is burned at around 1100˚C. © TREA Breisgau

How is electricity actually generated at TREA?

All waste is initially deposited in a bunker. A characteristic of residual waste is that it is very inhomogeneous, as everybody must be aware from the contents of their own bins, so some waste burns better than other waste. We have people whose job it is to mix the material as efficiently as possible with a remote controlled grabber. This results in the waste having a largely consistent heating value of around 10 megajoule per kilogramme, which is similar to that of brown coal. The stirred waste is then put into a combustion tank surrounded by tubes containing flowing water. Temperatures inside the tank reach between 1000 and 1100˚C . The waste is treated in the combustion tank for around an hour. The water in the tubes gets hotter and hotter, finally becoming steam with a pressure of 40 bar and a temperature of 400˚C. The steam is fed into a 15 Megawatt turbine. The turbine looks like an oversized fan with different types of ventilation. The bucket wheels are attached to a shaft driven by the steam; the energy from the shaft is transferred to a generator that converts it into electricity.

What is left over and what happens with this waste?

Virtually all the carbon in the waste is used up during combustion. What remains is slag, a mixture of silicates, calcium compounds and other compounds that cannot be burnt, for example around 7 per cent iron and slightly over 1 per cent of non-iron metals, that is then used for the production of materials. The slag is processed in a plant around 500 metres from here that is run by Schlackeverwertung Breisgau GmbH (SVB). Our company currently owns 51 per cent of SVB. The slag, which amounts to about 25 per cent of the initial waste, is used in road construction under sealed areas. However, the process generates something more than just solid residues. Gaseous contaminations such as chlorides, fluorides, furans and dioxins are isolated in a highly complex, several-tier flue gas purification process and nitrogen oxides are chemically degraded in a catalyser. The reaction products resulting from the treatment of flue gas and residual material are transported to disused salt mines in Thüringen, where they become landfill.

TREA Breisgau located in the Breisgau industrial estate is an example of a plant in which waste is burned for the generation of power. © Giera-Bay

What can be said about the environmental compatibility of generating electricity from waste?

The results obtained through the filtering and chemical conversion of gaseous residues comply with the conditions stipulated by the 17th Federal Emission Protection Regulation. However, when the regulation was put in place the then operators of TREA had far more ambitious goals: they wanted to halve the threshold values and so they decided to add a flue gas scrubber. This means that the gasses that leave the chimneys of other plants at temperatures of between 130 and 140˚C are fed into a wet scrubber at TREA where they absorb water and become visible in the form of steam. This steam mainly contains nitrogen and CO2 and of course also small concentrations of harmful substances, which are nevertheless way below legally stipulated thresholds. The German government has issued threshold values for dust, HCl, nitrogen oxides and mercury, all of which are monitored 24/7 at TREA. We are not only way below the threshold limits required by German regulations, the values we record are around 50% less than the legal thresholds stipulated in the authorisation to run the TREA facility. These low thresholds are the result of a very complex flue gas process and we are very proud of these values. What comes out of our chimneys is basically no more than water vapour, which for us is a clear indication of our facility’s high environmental standards.

How does the degree of efficiency and CO2 emission of waste combustion compare to other energy generation methods?

Assuming that a single household uses around 4,000 kilowatt hours per year, the electricity produced at TREA would be enough for around 25,000 households. We produce slightly over 100,000 kilowatt hours of electrical energy per year. The degree of efficiency is around 25 per cent; coal power stations have a degree of efficiency of around 38 per cent. The difference is mainly due to using waste as fuel which is unsuitable for high steam and temperature parameters due to corrosion. In addition, the lower level of efficiency of our plant is also due to the complex flue gas purification, which of course requires more energy. In terms of CO2 emission, the waste used at TREA consists mainly of biological waste. It is generally assumed that household waste consists of around 60 per cent of biogenic material. If the same amount of electricity were produced with a coal power station, a similar  level of CO2 would be emitted. However, because we use biogenic waste we also make a positive contribution to the environment because biogenic waste would otherwise just rot, a process that would generate methane, which is around 30 times more harmful than CO2.

Matthias Nawrat from Freiburg BioRegion interviewed Dr. Holger Heinig on behalf of BIOPRO Baden-Württemberg GmbH.

Background information:

Based on a European-wide open tender in December 2000, the Gesellschaft Abfallwirtschaft Breisgau (GAB) mbH commissioned a consortium of tenderers consisting of SOTEC GmbH (now EO.N Energy from Waste Saarbrücken GmbH) and SITA Deutschland GmbH (Cologne) to dispose of the residual waste accumulating in the municipal district of Breisgau-Hochschwarzwald and the city of Freiburg as well as of some of the waste collected by Zweckverband Abfallbehandlung Kahlenberg (ZAK). The contract was to run from 2005 onwards. E.ON Energy from Waste Saarbrücken GmbH subsequently constructed the Thermische Restabfallbehandlungs- und Energieerzeugungsanlage (TREA) Breisgau in the Breisgau industrial estate, which became operative in November 2004. The electricity produced by TREA is marketed by TREA Breisgau Energieverwertung GmbH (TBE), which consists of: Gesellschaft Abfallwirtschaft Breisgau (GAB) mbH (Freiburg) (awarding authority), E.ON Energy from Waste Saarbrücken GmbH (Saarbrücken) (operator), the regional community heating company Freiburger Wärmeversorgung GmbH (FWV) (Freiburg; a subsidiary of badenova AG und Co. KG and Evonik Industries AG) and the Breisgau Industrial Park.

Further information:

Dr. Holger Heinig
COO TREA Breisgau
Tel.: +49 76 34/50 79-110
Fax: +49 76 34/50 79-135
E-mail: Holger.Heinig1@eon-energie.com
E.ON Energy from Waste Saarbrücken GmbH
TREA Breisgau
Heitersheimer Str. 2
79427 Eschbach

Website address: https://www.biooekonomie-bw.de/en/articles/news/residual-waste-an-eternal-fire-that-generates-electrical-power